APPENDIX 259

of free alkali with standard acid, using phenolphthalein as
indicator. The difference gives the amount of alkali neutralised
by the fatty acid (see p. 210).
PREPARATION 29.
Formic Acid.—In addition to the method described, the
acid is formed in the decomposition of chloral (see p. 9),
chloroform (see Prep. 8, p. 71), by the action of cone. HC1 on
the isocyanicles,
C,H5NC + H20 = C,H5NHo + HCO.OH,
by the decomposition of aqueous hydrocyanic acid, which yields
the ammonium salt,
HCN + 2l-IaO = HCOONH4,
and by the oxidation of methyl alcohol with potassium bichrom-
ate and sulphuric acid. It is present in the sting of ants and
nettles, and is also occasionally found among the products of
bacterial fermentation of polyhydric alcohols and carbohydrates.
The commercial method is to act on solid NaOH with CO
under pressure and at a temperature of about 100° :
CO + NaOH = IICOONa.
The calcium salt is used in the preparation of aldehydes by
heating- it with the calcium salt of a higher aliphatic acid,
(HCOO)oCa -1- (CH3,COO)aCa = 2CH3CO.H + 2CaCO;;.
The reducing action of formic acid and' formates on metallic
salts may be ascribed to the presence of the aldehyde group
(OH)CH:O in the acid.
PREPARATION 30.
Allyl Alcohol.—Note the difference produced by the
change in the relative quantities of glycerol and oxalic acid,
and the temperature at which the reaction is brought about.
In the case of formic acid, it is the oxalic acid alone which
undergoes decomposition, and theoretically a small quantity of
glycerol will effect the decomposition of an unlimited amount
of oxalic acid. But at the higher temperature it is the glycerol
which yields the main product. Allyl alcohol being an un-
S 2